In the computerized weighing art, it is known to obtain a substantially precise target weight of a product charge formed of a plurality of individual charges having various weights, each of which is a significant fraction of the total desired weight. The state of the art of this "combination weighing" system is exemplified by the system in U.S. Pat. No. 4,538,692 to Henry et al., assigned to the assignee of the present invention.
In the Henry et al. patent, quantities of product having a portion of the target weight are distributed to a plurality of scale-controlled hoppers arranged in a circle. The weighed product is fed from each of the hoppers to a plurality of storage cups associated with each of the hoppers. The product weight associated with each storage cup is registered. Specific combinations of storage cups are scanned to determine whether the combined product weights therein add to make the desired weight (within an acceptable limit above the target weight). The first combination found to make the target weight is used, and the appropriate storage cups are emptied to a container for receiving the product.
While the Henry et al. method and apparatus have proved highly efficient and been successfully received in the marketplace, it must be recognized that this approach is particularly adapted for use with dry flowing product. In contrast, where a product is difficult to handle, such by being sticky and/or substantially irregular in size and shape, certain additional requirements are placed on the combination weighing system that are not addressed in the Henry et al. patent. It has been found that mass conveying and automatic filling of the product to make up the individual portions to be combined for the target weight is not efficient.
An example of a sticky, difficult to handle product is a meat product, such as beef tips. Conveying by vibratory feeders, as in the prior art, is very difficult because of the inefficient sliding action of the product in the feeder pans. Filling of the hoppers by the product sliding down a chute is also not practical for the same reason. To compound the problem, when this type "flowing" handling is attempted with sticky and irregular product, such as the beef tips, tallow and other product matter gradually build up on the apparatus components including the feed conveyor, scale hoppers, storage cups, feed chutes and the like. The problem is such that even over a relatively short period of time, a certain point is reached where the weighing performance of the apparatus is so severely degraded that the desired target weight is essentially unobtainable.
Under these operating conditions, the primary concerns in designing the combination weighing apparatus are to (1) provide relatively accurate portions of the sticky/irregular product to be weighed in the hoppers; (2) minimize the surface contact between the apparatus and the product during handling and (3) minimize the number of product transfers necessary to complete the weighing and delivering operation. These primary concerns must be addressed without adversely affecting the ability to provide product with the desired target weight during continuous machine operation over extended periods of time.